The inside story of trees

It has been well over a month since Hurricane Sandy, and we still hear the buzzing roars of chain-saws in backyards, along streets and utility right-of-ways.

It has been well over a month since Hurricane Sandy, and we still hear the buzzing roars of chain-saws in backyards, along streets and utility right-of-ways.

Massive uprooted trees, heavy fallen limbs and behemoth tree trunks snapped in half like fragile toothpicks remain as visual reminders of the power and destruction of hurricanes.

Hurricane Sandy repainted the Pocono landscape. However, along her broad path of destruction she opened a door to an environmental classroom. If you want to learn about tree biology, now is an opportune time.

There are many questions to be asked and answers to be found.

You notice that the large white pine that had snapped in half and fallen in your back yard was hollow inside. You ask, "If it was hollow on the inside, why did it look so healthy on the outside?"

The bright yellow-orange of a freshly cut oak limb catches your eye as you walk your dog along your favorite country road. You notice that the tree was cut because it obstructed a utility right-of-way. Closer inspection of the limb reveals circular rings and various shades of color extending into the thick, furrowed bark. You already know that the tree rings signify annual years of growth, but ponder: "Why are there different shades of color?"

During a hike in a wooded park, you see a large eastern hemlock toppled over in a soggy wetland. You admire its large root base but question: "Why are the roots so wide and close to the surface and not deep into the ground?"

These are all intriguing questions and many may know the answers, but some of us do not. Here, I will share information about tree biology and why that healthy hollowed tree fooled you, circle in some facts on colorful trees rings and dig more deeply into tree roots.

Let's first start off with basic tree anatomy — the trunk, limbs and roots. The growth of a tree begins with its root system. Tree roots are like underground branches; they have large roots including the tap root and many small, fibrous roots. Tree roots serve several functions such as absorption, storage and transportation of water and minerals to the entire tree. The larger roots provide stabilization and anchoring to support and keep upright the trunk, limbs and branches. The tiny, fine roots aid in nutrient and water absorption.

Remarkably, trees roots grow wide and close to the surface, such as on that toppled eastern hemlock you asked about. There is a misconception that trees have a tap root that grows as deep as the height of the tree. Certain trees such as oaks develop a tap root; however, most trees have a root system that grows inches from the surface to a only few feet deep. Tree root systems, for the most part, grow wider than the crown of the tree — especially in wetlands.

Now let's study the multi-colored growth rings on the freshly cut oak limb you found along the road. Each individual annual growth ring consists of two shades — a light color which grows in the spring and a dark color which grows in late summer. The entire series of rings on the oak tree is surrounded by a thick layer of dark-colored bark. Also, the tiny center ring of the tree is dark colored. This is called the heartwood, which is the hardest and strongest part of the tree. The outer rings extending toward the bark are called the sapwood. Ironically, each inner growth ring starting from the heartwood was once living tissue but is now dead. Each year a ring of new wood grows and last year's wood dies and becomes harder, which provides support to the tree. The only living layer of wood occurs near the bark. Sometimes those inner multi-colored rings of dead wood rot and decompose due to various reasons such as fungus, moisture, disease and insects, which might cause the tree to become hollow.

This brings us to the question: "Why did the white pine that toppled into the backyard look healthy on the outside, even though it was hollow on the inside?"

On a typical tree, the hard series of growth rings were once layers of living tissue. However, between the dead inner wood and the outer bark are the growth cells called the cambium layer. The cambium is composed of two tissues, the xylem and phloem. These are important cells which supply and transport nutrients throughout the tree.

The phloem layer occurs along the outermost side of the tree, next to the bark. Its main function is to transport sugars made by green leaves and other nutrients collected by the tree down into the roots.

The xylem, the innermost cells of the cambium, transport water, minerals and nutrients from the root system up to the tallest branches and leaves on the tree.

Each year, the xylem layer dies and forms hardwood, while the phloem is always alive and provides the wide new growth of the trunk and other parts of the tree. If the cambium layer is disrupted — for example, a woodpecker drills a hole into the tree — nutrients can still be transported along the unobstructed areas of the cambium layer. However, if a hungry beaver girdles entirely around the tree and its cambium layer — the nutrient pipeline — is cut off, the tree will eventually die.

So, in spite of all of that dead inner wood on the white pine, which became hollowed-out for whatever reason, the cambium layer still allowed the tree to live and appear healthy on the outside. Unfortunately, its structurally supportive center core was hollow and easily snapped in half during Hurricane Sandy.

I hope this analogy helps broaden your understanding of trees and what makes them grow and remain strong and spectacular. Sometimes natural events, such as hurricanes, are not in our best interest — nor for the trees that stand in its way. Whatever the outcome, there's always an opportunity to learn a little bit more about nature.

Contact Rick Koval at pocononaturalist@yahoo.com or write to him at PO Box 454, Dallas, PA 18612.

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